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<p>Sheared peridotite xenoliths entrained by kimberlites provide snapshots of metasomatism and deformation within the cratonic mantle. Here, we present H<sub>2</sub>O concentrations of nominally anhydrous minerals (olivine, orthopyroxene and clinopyroxene) in 18 low-, moderate- and high-T sheared peridotites from the Kimberley and northern Lesotho kimberlite cluster (Kaapvaal craton). H<sub>2</sub>O contents range from &lt; 1–80&#xa0;µg/g (olivine), 70–310&#xa0;µg/g (orthopyroxene) and 120–300&#xa0;µg/g (clinopyroxene), implying hydration through metasomatism. Core to rim heterogeneities in H<sub>2</sub>O concentrations indicate that ortho- and clinopyroxene cores preserve an older metasomatic/deformation event in the lithospheric mantle while olivine cores record the youngest metasomatic event. The latter must have happened immediately prior to xenolith entrainment and transport to the surface. Calculated H<sub>2</sub>O contents for the metasomatic agents range from 1 to 3 wt% H<sub>2</sub>O. We speculate that highly-reactive hydrous (proto-)kimberlitic melts caused oxidizing metasomatism that triggered deformation prior potentially enhanced craton destabilization as well as the local resorption of diamonds.</p>

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The H2O component of sheared mantle peridotites from the Kaapvaal craton: evidence for hydrous deformation with implications for the stability of cratons

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  • 发表日期：

    2026年1月24日

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  • Catharina Heckel,
  • Anthony C. Withers,
  • Alan B. Woodland,
  • Sally A. Gibson,
  • Thomas Ludwig

摘要

Sheared peridotite xenoliths entrained by kimberlites provide snapshots of metasomatism and deformation within the cratonic mantle. Here, we present H2O concentrations of nominally anhydrous minerals (olivine, orthopyroxene and clinopyroxene) in 18 low-, moderate- and high-T sheared peridotites from the Kimberley and northern Lesotho kimberlite cluster (Kaapvaal craton). H2O contents range from < 1–80 µg/g (olivine), 70–310 µg/g (orthopyroxene) and 120–300 µg/g (clinopyroxene), implying hydration through metasomatism. Core to rim heterogeneities in H2O concentrations indicate that ortho- and clinopyroxene cores preserve an older metasomatic/deformation event in the lithospheric mantle while olivine cores record the youngest metasomatic event. The latter must have happened immediately prior to xenolith entrainment and transport to the surface. Calculated H2O contents for the metasomatic agents range from 1 to 3 wt% H2O. We speculate that highly-reactive hydrous (proto-)kimberlitic melts caused oxidizing metasomatism that triggered deformation prior potentially enhanced craton destabilization as well as the local resorption of diamonds.